The present invention relates to an Electrostatic Precipitator that is particularly adapted for use in connection with diesel engines for removing particulate matter from crankcase gases prior to venting the gases to the atmosphere or returning the gases into the intake manifold for exhaust gas recirculation. More particularly, the present invention relates to certain improvements in the high voltage power supply to make it more suitable for Diesel blowby gas filtration. The invention also relates to mounting the high voltage power supply in a separate housing that can be completely separated from the precipitator electrode and electrode housing in a manner that minimizes the likelihood of a continued high voltage charge on the electrode as the power source housing is removed from the electrode housing.
U.S. Pat. No. 6,221,136 describes a compact, high efficiency electrostatic precipitator for collection of aerosols containing suspended droplets and particles in a gas. As the dirty gas containing suspended droplets and other forms of particulate matter is passed through the precipitator the droplets and other forms of particulate matter are charged by the corona ions generated by a high voltage electrical discharge from a fine wire. Some of the particles may also carry a natural electrical charge as a result of the particle formation process in the Diesel engine combustion chamber and the blowby gas in the crankcase. The applied high voltage then causes the charged droplets and particles to migrate toward an adjacent grounded surface where they are collected, and the droplets and particulates are allowed to drain off by gravity to a sump.
The electrostatic precipitator section disclosed in U.S. Pat. No. 6,221,136 is particularly suited for use with a Diesel engine to remove suspended droplets and particles from a blowby gas. The blowby gas has its origin in the high temperature, high-pressure combustion gas formed inside the combustion chambers of the Diesel engine. Some of this high-temperature, high-pressure gas can leak past the piston rings of the Diesel engine to the crankcase. This gas contains both unburned Diesel soot as well as lubricating oil droplets formed as the blowby gas flows past the piston rings, where it encounters and atomizes the lubricating oil film to form droplets. The blowby gas thus contains both lubricating oil droplets as well as unburned Diesel soot.
In the past, the blowby gas usually was vented to the atmosphere directly. Concerns about air pollution from motor vehicles in general, and from the Diesel-powered vehicles in particular, have led to regulations that would require particulate emissions from Diesel engines to be greatly reduced. The electrostatic precipitator described in U.S. Pat. No. 6,221,136 is particularly suited for this application because of its small and compact size, its high efficiency for droplet and particle collection, and the low pressure drop created by the blowby gas as it flows through the device for droplet and particle removal.
In addition, the electrostatic precipitator collects not only the suspended oil droplets in the blowby gas, but also the dry, solid Diesel soot. The dry soot particles normally would cling to the surface on which they are collected. However, in the presence of oil drops in the blowby gas from a Diesel engine, a thin film of oil is formed on the collecting surface. The soot particles are thus collected onto this liquid thin film and are carried away as the oil film drains off from the collecting surface by gravity, thus returning both the oil and Diesel soot into the crankcase of the engine. As a result, the collecting surface in the electrostatic precipitator can remain relatively clean over long periods, thus insuring the reliable operation of the device over a long lifetime.
The operation of the electrostatic precipitator is dependent upon a power source to provide a high-voltage DC power to the high voltage electrode in the electrostatic precipitator. The DC high voltage needed may range up to 20,000 volts or more. The presence of this high voltage must be addressed in order to avoid accidentally having a person come in contact with the high voltage. The high voltage DC power source may also cause arcing and the emission of electromagnetic waves that can interfere with the engine control computer and other sensitive electronic circuitry nearby. For these reasons, the design of the high voltage power supply and its coupling to the electrostatic precipitator in Diesel blowby applications are both very important.